Untargeted mass spectral profiling of water soluble propolis extracts from acid and alkaline hydrolysis

Abstract

This study was aimed to prepare water soluble propolis with high antioxidant capacity. Process preparation for good quality and safe propolis has yet to be established and standardized. Different extraction techniques and solvents have intensively been investigated, but ethanolic propolis is preferable due to the high yield of phenolic compounds. However, ethanolic propolis always comes along with indigestible resinous substance. The present study incorporated an additional step of hydrolysis to increase the solubility of resinous substance in propolis. Acid (pH 3) and alkaline (pH 8) hydrolysis were performed and compared for their effectiveness to increase water soluble phenolics including flavonoids. Alkaline hydrolysis was effective to increase phenolics (6 times), flavonoids (2 times) and tannins (5 times). Only 2 times increment of phenolics by acid hydrolysis. Alkaline hydrolysis was prone to cleave inter-molecules bonds, whereas acid hydrolysis was likely to cleave glycosidic bonds. The chromatographic and mass spectrometric profiles also revealed that alkaline hydrolysed propolis extract (KPE) had more phenolics and flavonoids than acid hydrolysed propolis extract (CPE). Besides resveratrol and hydroxyscopoletin derivatives, KPE was found to have few glycosylated ellagic acid and flavones, as well as galloylated flavonoids which were likely to be radical scavengers. Unsupervised statistical approach was significantly clustered KPE away from CPE based on mass spectral data. Therefore, alkaline hydrolysis was more effective to prepare water soluble propolis extract with higher antioxidant capacity.